1. Tina S. Morris, Ph.D., Vice President Biologics & Biotechnology USP-NF
Biological Assays
Tina S. Morris, Ph.D., Vice President
Biologics & Biotechnology USP-NF
User Forum
January 17th, 2013
Istanbul, Turkey

2. From General to Specific – Biological Potency
<1030> Overview of Bioassay
Guidance & Information
<1032> Development of Biological Assays
<1034> Analysis of Biological Assays
<1033> Validation of Biological Assays
<111> Design and Analysis of Biological Assays
General
Requirement
Product-Specific
Requirement
<121> Insulin Assays
Product Quality Attributes
Insulin Monograph

3. USP Bioassay Chapters Official since 1950: The new suite:
<111>: Design and Analysis of Biological Assays
Will be substantially revised soon
The new suite:
<1030>: Biological Assay Chapters – Overview and Glossary PF 38(4)
<1032>: Design and Development of Biological Assays
<1033>: Validation of Biological Assays
<1034>: Analysis of Biological Assays
All of these chapters are focused on relative potency bioassays.
Note chapter numbering! This is important.
Official

4. 5.50.10. Units of Potency (Biological)
A Word on Units
USP General Notices:
Units of Potency (Biological)
For substances that cannot be completely characterized by chemical and physical means, it may be necessary to express quantities of activity in biological units of potency, each defined by an authoritative, designated reference standard.
Units of biological potency defined by the World Health Organization (WHO) for International Biological Standards and International Biological Reference Preparations are termed International Units (IU). Monographs refer to the units defined by USP Reference Standards as “USP Units.” For biological products, units of potency are defined by the corresponding U.S. Standard established by FDA, whether or not International Units or USP Units have been defined

5. The Use of IU in USP Monographs

6. Product-Specific Potency Assays
Can be called out in a Monograph or General Chapter
Monograph requirements supersede Chapter Requirements
A potency test or at least bioidentity test based on a functional assay is required for most biologics and biotechnology-derived medicines licensed in the US market

7. Assay – Amount of Substance or Activity?
ICH Q6B:

8. Europe and the US Differ in Bioassay Requirements
In Europe, for peptides and small proteins that are considered “well-characterized” neither a unit-based quantitative bioassay nor a bioidentity test are required. This is not the case in the US.
Some examples:
Insulin(s) - US requires bioidentity based on USP <121>: rabbit blood glucose test
Somatropin - US requires rat weight gain assay
Glucagon - US requires primary rat liver cell assay, USP <123>

9. Compendial Implications
Many bioassays and bioidentity tests for licensed biologics are still animal-based.
Associated concerns:
Assays with generally high variability and poor precision
Challenges in unit assignments and maintenance, especially in relationship to the International Unit where it exists
Ethical issues regarding animal use

10. USP Initiative: Replacement of Animal Assays
<123> Glucagon Bioidentity Tests – USP will add a cell-based assay to this chapter and distribute the necessary cell line as a reference standard
<126> Somatropin Bioidentity Tests – USP is currently evaluating a cell-based assay using a nonproprietary cell line. The chapter will contain the animal test and the cell assay initially
<121> Insulin Assays – USP has received and will begin evaluating a cell-based assay for insulins

11. Case Study: Heparin Potency
Anti Factor IIa chromogenic assay replaced the sheep plasma clotting assay for potency assignment in stage 2 revision of Heparin Sodium monograph, official since October 1st, 2009
Minor revision to PF 33 (2) test incorporating recommendations from the Advisory Panel
Validation study was conducted on revised PF 33 (2) test
Incorporation of an anti-factor Xa/ anti-factor IIa ratio specification: NLT 0.9 and NMT 1.1
New Acceptance criteria: The potency of Heparin Sodium, calculated on the dried basis, is NLT 180 USP Heparin Units in each mg.
USP harmonizes units with IU when USP Heparin Sodium for Assays RS, Lot F, was introduced in July 2009

12. Anticoagulant actions of heparin
Heparin Co factor II
Unfractionated Heparin
LMW Heparin
Heparan sulphate
TFPI
Antithrombin

13. Anticoagulant activities of sulphated polysaccharides
Heparin Co factor II
Unfractionated Heparin
LMW Heparin
Heparan sulphate
Dermatan sulphate
Oversulphated chondroitin sulphate
Chitosan sulphate
Dextran sulphate
TFPI
Antithrombin

14. Clot-Based Activity Assays for Heparin
Not specific for heparin; will detect any anticoagulants that prolong clotting times
EP and USP (pre-October 2009) assays, use sheep plasma as substrate; highly influenced by other sulphated polysaccharides
APTT using human plasma as substrate; less influenced by other sulphated polysaccharides than sheep plasma assays
Others e.g. thrombin time
It is well established that only heparin and heparan can potentiate the inhibitory activity of antithrombin, so the use of antithrombin dependent chromogenic substrate assays will prevent the adulteration of heparin with materials that can only increase anticoagulant activity by potentiating the action of heparin co-factor II.

15. Specific Activity Assays for Heparin
Mostly chromogenic substrate assays:
Antithrombin dependent anti-Xa and anti-IIa assay, will work for heparin, LMW heparin and heparan sulphate; not influenced by other polysaccharides that potentiate heparin co-factor II
Heparin co-factor II dependent anti-IIa assay, will work for heparin, LMW heparin and other polysaccharides that potentiate heparin co-factor II
Anti-Xa and anti-IIa assays that use plasma as a source of antithrombin. Depending on the protocol, anti-IIa activity can be influenced by the presence of other polysaccharides
It is well established that only heparin and heparan can potentiate the inhibitory activity of antithrombin, so the use of antithrombin dependent chromogenic substrate assays will prevent the adulteration of heparin with materials that can only increase anticoagulant activity by potentiating the action of heparin co-factor II.

16. Changes in Specific Activities of Heparin
Typical specific activities of unfractionated heparin from the 80s or earlier were around 150 U/mg while those produced in the 90s or later are typically close to 200 U/mg
The international, EP and USP standards and especially the USP standards (Lot K series) issued in the early 90s have much lower specific activities – around 150 U/mg
Molecular weight distributions of these standards were also different to the “modern” clinical products
This meant that the assay of these clinical UFH against these standards was getting away from the important principle of bioassays- LIKE against LIKE – leading to inaccurate estimation of potency

17. Influence of Impurities
Impurities such as dermatan can potentially influence the anticoagulant potency of UFH estimated by plasma based assays:
Compete for PF4 and other heparin binding proteins
Potentiate inactivation of thrombin by heparin co-factor II

18. Antithrombin Dependent Chromogenic Assays
Anti-IIa assay
IIa
IIa Substrate
pNA AT
Hep Xa
Xa Substrate
pNA
Anti-Xa assay
Simple Enzymatic Assays!

19. Potentiation of Antithrombin Activity
Pentasaccharide is sufficient for
inhibition of Xa
>18 saccharide is required for
inhibition of IIa 19 19

20. Anti-Factor IIa Assays by USP Method: Laboratory Variation
%GCV
Lab T V W X Y Z 02
6.2
3.5
2.5
1.4
1.8
3.7 03
7.6
13.6
12.9
16.3
6.1
7.1 06
6.8
4.6
4.5
2.4
7.5 08
2.6
3.1
2.8
8.4
3.6 12
1.5
6.7
6.0
2.0 13
8.5
10.9
7.3
6.6 19 .
29.1
9.2
23.4
9.3 25
5.3
1.7
3.0
5.4 32
8.1
1.9
2.9
Range = 1.4 – 29.1 %; 27/52 < 5%; 44/52<7%; 46/52 <10%
Data from collaborative study to value assign 6th International Standard for Unfractionated Heparin

21. Implementation of New Potency RS
Reference Standard was issued as Lot F, Heparin Standard for Assays – this allowed USP to have the stillcurrent potency standard and the new standard available simultaneously for industry transition.
Reference Standard has been calibrated relative to the 5th International Standard for UFH.
Assignment of potency value is based on the proposed chromogenic Anti-factor IIa assay
Standard has been available as of July 22, 2009.

22. Assay Transition Challenges - Heparin
Transition from a non-specific to a highly specific test
Old compendial test and reference standard were not linked to an International Standard (IS) and USP potency unit over time (+30 years) had drifted away from the IU by approximately 10%
Product is still dosed in units – any adjustment to the potency has immediate practitioner and patient impact
Fast-tracked introduction of the new assay and reference standard during a public health crisis – introduction of new test and standard required close coordination with FDA and industry

23. USP heparin Expert Panel & USP Heparin Staff Team

24. Challenges to Product-Specific Compendial Bioassay Development
Conclusions – what are the key challenges?
Equivalence determination between assays:
Challenges in establishing equivalent results between different biological systems: animal vs. cell-based assays etc.
Assays for biological products with more than one activity
Commutability of assays and reference materials
Availability of public methods and data:
Intellectual property barriers

25. Thank you!
As you can see from the world map on the outside of USP headquarters building, it is a global pharmacopeia based in Rockville, Maryland. No borders.